Project Summary: Natural selection for the ability to assign perceived sounds to their correct sources in the environment was a major force driving the early evolution of the vertebrate auditory system. Consequently, we share with non-human vertebrates many of the basic mechanisms responsible for sound source segregation. These mechanisms function in solving the familiar "cocktail party problem" of perceiving speech in the presence of multiple talkers. The users of hearing aids and cochlear implants usually find that their devices provide little or no improvement in speech perception in loud social environments. The long-term goal of the proposed research is to integrate behavioral and electrophysiological experiments in a lower- vertebrate model to achieve a better understanding of the basic signal processing strategies by which vertebrate auditory systems segregate vocal communication signals in noisy social environments. Frogs are a superb model for investigating sound source segregation because reproductive behaviors in this group are mediated by the perception of vocal signals (mating calls) in noisy social aggregations (breeding choruses). That is, frogs must solve their own cocktail-party-like problem to successfully reproduce. This project addresses two specific aims using well-established methods to elicit behavioral responses from female gray treefrogs (Hyla versicolor) to male mating calls: 1. Identify acoustic properties that promote auditory stream segregation of overlapping vocal signals. The working hypothesis for this aim is that differences in fundamental frequency and other acoustic properties of mating calls allow the frog auditory system to segregate the temporally overlapping vocal signals of nearby calling males in a chorus into separate auditory streams. 2. Identify mechanisms for segregating target signals from biologically realistic masking noise. The working hypotheses for this aim are that (i) spatial separation between target signals and "chorus- shaped" noise leads to spatial unmasking and (ii) frogs experience a release from masking by "listening in the dips" of chorus-shaped noise maskers with the modulation statistics of a real chorus. Relevance: A better understanding of how vertebrate auditory systems achieve sound source segregation in noisy social aggregations will lead to advances in the design of hearing prosthetics that improve the ability of the hearing impaired to navigate social interactions in a noisy world. Results from this study, and future related projects that will integrate behavior with electrophysiological methods, are expected to generate new and deeper insights into the mechanisms of sound source segregation in a lower vertebrate model that has evolved to contend with a well-known animal equivalent of the cocktail party problem. [unreadable] [unreadable] [unreadable]